In hypersonic vehicles, understanding the transition of the boundary layer is crucial to the design of the thermal protection system due to the significantly higher drag and heating rates of turbulent boundary layers. However, the nature of the thermal protection system can affect the stability and transition prediction of the boundary layer. Many thermal protection systems use ablation as a means of controlling vehicle temperature. These systems add new species to the boundary layer and change the chemistry of the flow. Carbon-based ablators have gained popularity due to their smooth ablative and heat transfer characteristics. The addition of carbon species, specifically CO_2, into the boundary layer of a hypersonic vehicle has known damping effects on the high frequency second mode disturbances that dominate in this flow regime. This study examines the impact of CO_2 in the boundary layer from ablation by using common gas-surface ablation models as the wall boundary condition in computational fluid dynamics simulations. The study was conducted on both blunted and sharp cone geometries. The results show that at the current concentrations of CO_2 created from the ablation models, there is limited effect of molecular damping on the stability of the boundary layer, seen only in the amplification of specific frequencies but does not contribute to an overall increase in stability. Furthermore, the geometry of the blunted nose has more on an impact on the stability due to the creation of an entropy layer which masks the effect of CO_2 damping.
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